1. Field of the Invention
The present invention relates to a supporting structure of a shaft of a reduction gear.
Priority is claimed on Japanese Patent Application No. 2008-262117, filed Oct. 8, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
A structure, as shown in FIG. 4, which supports a pinion shaft 14 at the tip of which a bevel pinion 12 is formed in a reduction gear 10 is disclosed in Japanese Unexamined Patent Application Publication No. 2006-207828 (FIG. 2). The reduction gear 10 includes a speed reduction mechanism 13 (only a portion is shown) having the inscribed meshing planetary gear structure at its preceding stage, and the pinion shaft 14 is connected with a carrier 16 which is an output shaft of the speed reduction mechanism 13 at the preceding stage via a spline 18. Further, the pinion shaft 14 is supported by a casing 27 by a tapered roller bearing 24 disposed almost at the center of the pinion shaft 14, and a tapered roller bearing 26 disposed at a cylindrical portion 16A of the carrier 16 via the carrier 16. That is, the load in a radial direction and the load in a thrust direction applied to the pinion shaft 24 are shared and received by both the tapered roller bearings 24 and 26.
On the other hand, a reduction gear 28, as shown in FIG. 5, which supports a bevel pinion 32 integrated with a joint shaft 30 by one pair of ball bearings 34 and 36 is disclosed in Japanese Unexamined Patent Application Publication No. 2007-211920 (FIG. 1). The axial movement of one pair of ball bearings 34 and 36 is restrained by a stepped portion 38A of the casing 38, a stage portion 30A of the joint shaft 30, and a retaining ring 40. In this reduction gear 28, the thrust loads in an A direction and in a B direction generated in the bevel pinion 32 are received by one pair of ball bearings 34 and 36 whose axial movement have been restrained.
As such, when a shaft which generates a thrust load, especially during operation, like a shaft including a bevel pinion, is supported by the casing of the reduction gear, a supporting structure which can simultaneously cope with the load in the radial direction and the load in the thrust direction is required.
Therefore, a configuration in which the shaft is supported at both ends by one pair of bearings in order to receive the radial load and a configuration in which the axial movement of an inner ring or outer ring of a bearing is restrained in order to receive the thrust load are required, and it is necessary to increase the span of one pair of bearings in order to secure stable support. As a result, there is a problem in that axial length becomes large.